In some other programming languages, enumerations are built using another underlying type. For example, in C++, enumerations are actually a set of integers.

The Swift implementation of enumerations is much more flexible, allowing you to assign a raw value to each case. You can assign Strings, Characters, Ints, Doubles, and Floats as a raw value. However, you can only assign one raw value type per enumeration. This could be useful for situations where each case has a value attached to it that is used by your code logic in some capacity.

enum Emoji: String {
    case bee = "🐝"
    case brain = "🧠"
    case heartEyes = "😍"   
}

By using the : String syntax and the assignment operator =, we explicitly assign each of the Emoji enumeration cases underlying raw String values.

We access the raw values using the .rawValue property.

print(Emoji.brain.rawValue) // Prints: 🧠

If we use Int or String raw values, we can also implicitly assign values for each case by explicitly assigning the first case like so:

enum Team: Int {
    case alpha = 1
    case bravo
    case charlie
    case delta
}

print(Team.delta.rawValue) // Prints: 4

Because the first case, alpha, is assigned the integer value of 1, the compiler infers that bravo should have a raw value of 2 and so on. If you use Strings as raw values and do not explicitly assign a value, the compiler will use the name of the case as its raw value.

Once we assign raw values for an enumeration, we can then initialize an instance using a raw value like so:

enum Weekday: Int {
    case monday = 1 
    case tuesday 
    case wednesday 
    case thursday 
    case friday
}

let birthday = Weekday(rawValue: 3)

// birthday is of type Weekday? and equals Weekday.wednesday

You might be wondering what the question mark on Weekday? means. The ? symbol indicates an Optional type which means the value can either be some value or a nil value. We will be covering Optionals in-depth in a later lesson, but you can learn more about them here.

Because it is possible that someone enters a raw value that isn’t assigned to any case in the Weekday enumeration, initializing from a raw value can return nil.

If you create an enumeration with String raw values and don’t provide any values, the raw value will be the same as the case name:

enum Status: String {
    case complete
    case pending
    case rejected
}

let myStatus = Status.complete
print(myStatus.rawValue) // Prints: complete